The present invention relates to a method of driving a stepping motor such as for use in mechanical positioning control, and more particularly to a method of driving a stepping motor in which excited phases are supplied with intermittent currents in the form of pulse signals while the motor is being stopped.
Stepping motors are driven by a known drive pulse generator circuit which is supplied with drive pulses to generate excitation signal pulses in the order in which the motor phase windings are to be excited, the excitation signal pulses being amplified and successively applied to the motor phases. The speed of rotation of the stepping motor is therefore dependent on the frequency of the drive pulses applied.
The rotation of the stepping motor is stopped when no drive pulses are fed to the motor. Upon stoppage of the supply of drive pulses, an excitation pulse generator circuit continues to excite a selected set of phases with the drive pulses impressed immediately before intermittent drive pulses are cut off.
Where the stepping motor is to be rotated at high speed with drive pulses having an increased frequency, it is customary to apply a voltage greater than a rated voltage to each phase of the motor for thereby improving motor characteristics during high-speed rotation. With such a practice, a voltage higher than a rated voltage is impressed on the windings of excited phases while the stepping motor is being held in a stopped position. When the motor is stopped for a long interval of time, excessive currents pass through the excited phases, resulting in the danger of burning out these windings. To solve this problem, Japanese Patent Laid-Open Publication No. 56-15189 discloses a stepping motor stop control system in which excited phases of a stepping motor are supplied with intermittent currents while the motor is being stopped, to thereby prevent the motor windings from being burned out.
When the stepping motor is started with drive pulses of a high frequency applied to the motor as it is stopped while the motor undergoes a load counteracting the motor rotation, the motor is liable to lose step and cannot start smooth rotation.